Device for simulating the original shape of a signal which is distorted by peaks

ABSTRACT

A device for simulating a distorted, exponentially decaying part of an input signal, comprising an RC-network having a controllable RC-time and a measuring member which converts the difference between the input signal and the generated signal into a control signal for the RC-network.

United States Patent Janssen et al.

[ 1 ,lan.7, 1975 DEVICE FOR SIMULATING THE ORIGINAL SHAPE OF A SIGNAL WHICH IS DISTORTED BY PEAKS Inventors: Frits Jacques Janssen, Waalre;

Arnold Lehmann, Emmasingel, Eindhoven, both of Netherlands U.S. Philips Corporation, New York, NY.

Filed: Mar. 5, 1973 Appl. No.: 338,050

Assignee:

[30] Foreign Application Priority Data Mar. 16, 1972 Netherlands 723463 [52] US. Cl. 328/162, 128/205 F, 128/21 R, 235/92 FL, 235/183, 328/127, 328/142, 328/164 [51] Int. Cl H03b 1/00, H03k 5/00, H04b 1/10 [58] Field of Search 328/144, 145, 60, 13, 15, 328/127, 142,143, 162, 164, 165; 235/183,

92 FL; 128/205 F, 2.1 R

[56] References Cited UNITED STATES PATENTS 2,946,012 7/1960 Patchell 328/144 3,255,417 6/1966 Gottliebl... 328/145 3,269,386 8/1966 Sherman l 128/2 3,304,413 2/1967 Lehmann et al. 235/92 FL 3,433,935 3/1969 Sherman 235/183 3,521,082 7/1970 Wolk 328/145 3,651,318 3/1972 Czekajewski 328/142 Primary Examiner-Stanley D. Miller, Jr. Attorney, Agent, or Firm-Frank R. Trifari; Bernard Franzblau 57] ABSTRACT A device for simulating a distorted, exponentially decaying part of an input signal, comprising an RC- network having a controllable RC-time and a measuring member which converts the difference between the input signal and the generated signal into a control signal for the RC-network.

8 Claims, 11 Drawing Figures I PATENTED'JAN mrs sum 10F 4 PATENTED JAN H975 sum 2 or 4 Fig.5

PMENTED AN ms SHEET 0F 4 v +VB DEVICE FOR SIMULATING THE ORIGINAL SHAPE OF A SIGNAL WHICH IS DISTORTED BY PEAKS The invention relates to a device for simulating the shape of an unknown signal which consists mainly of a peak which is followed by a decaying part, at least the first portion of said decaying part decreasing exponentially and a subsequent portion of said decaying part eventually being distorted, the said device comprising an output conductor which can be connected, via a first switching member, to either an input conductor which serves to supply the unknown signal, or the output of a signal generator which is adapted to generate an exponentially decreasing signal so as to simulate the decaying part of the unknown signal without the distortion, the said signal generator comprising a capacitor which can be discharged via a resistance element and which can be connected to the said input conductor.

A device of this kind is known from U.S. Pat. No. 3,375,701. The known device is intended for the simulation and subsequent integration, by means of an integrator, of signals whose shape and instant of occurrence of the disturbing peaks are accurately known, such as the signals which are produced by a gas chromatograph in which a sample is analyzed whose constituents are known or anticipated, but whose quantities must be measured.

However, the known device is not suitable for the simulation of a signal about which it is known only that it consists of a peak, followed by an exponentially decaying part, the said decaying part having an unknown time constant which, moreover, can differ from one case to another, while the decaying part can be distorted, for example, by peaks, the instant of occurrence of which is not known either. A signal of this kind is obtained, for example, with given methods of determining the heart minute volume of humans or animals, that is to say, the volume of blood which is displaced by the heart per minute. According to these methods, a quantity of some indicator substance (for example a dye) is injected into'the venous part of the blood circulation. This indicator gradually mixes with the ,blood during its passage through the circulation system so that it becomes increasingly less defined and further diluted until the indicator is finally homogeneous with the blood. If the variation of the indicator concentration is measured somewhere else in the blood circulation by means of a suitable measuring instrument, and the measuring result is plotted as a function of time on a graph, generally a dilution curve is obtained which comprises a first peak, followed by an exponentially decaying part on which one or more subsequent peaks appear. These latter peaks, referred to as recirculation peaks, are caused by the fact that the circulation system is closed and the indicator apparently performs a few rounds be fore it has been completely mixed with the blood.

In order to determine the heart minute volume, it is assumed that the circulation system is not closed, and the exponentially decaying part of the dilution curve is asymptotically extrapolated to zero. The curve thus obtained is the primary dilution curve. The heart minute volume V can now be determined from the relation of the injected quantity of indicator 1 and the surface area below the primary dilution curve according to the formula:

Lil

Therein, K is a constant and Sc(t)dt is the surface area below the primary dilution curve c(r).

An object of the invention is to provide a device which is capable of simulating the primary dilution curve on the basis of the dilution curve comprising disturbing recirculation peaks. The invention is based on the recognition of the fact that between the first peak and the first recirculation peak the dilution curve generally varies in accordance with the primary dilution curve for some time, and that this part of the dilution curve can be utilized to determine the time constant of the exponentially decaying part. It is then possible to utilize the said time constant in the subsequent generation of the remainder of the decaying part of the primary dilution curve. I

The device according to the invention is characterized in that the time constant of the network formed by the resistance element and the capacitor can be adjusted so that this time constant is matched to that of the decaying part of theunknown signal, a second periodically operating switching member being provided so as to establish the connection between the input conductor and the capacitor, the input conductor and the output of the signal generator being each connected to one of the inputs of a measuring member which is adapted to determine the difference between the signal generated by the signal generator and the unknown signal.

As soon as the measuring member indicates that the variation of the generated signal is the same as that of the decaying part of the unknown signal, the first switching member can be operated, after which the generated signal instead of the unknown signal is applied to the output conductor. It is obvious that the time constant of the signal generator is no longer varied as of that instant.

In a further embodiment of the device according to the invention, this switching operation is effected fully. automatically. This embodiment is characterized in that the measuring member comprises a first integrator for integrating a signal which is proportional to the difference between the unknown signal and the generated signal, the output of said first integrator being connected to a control input of the signal generator, the time constant of the resistor-capacitor network of the signal generator being dependent on the voltage on this control input. a

As already stated, in many cases the surface area below the curve representing the signal is required. This surface area can be determined by connecting the output conductor of the device to an integrator as is already done in said U.S. Pat. No. 3,375,701. A drawback of a device thus obtained is that a long period of time is required before the exponentially decreasing signal becomes so small that it no longer makes a significant contribution to the integration. This waiting time can be substantially reduced without a loss of information by constructing the device such that an amplifier is provided between the output of the signal generator and the first switching member, the amplification of said amplifier being equal to two. The output of the amplifier is connected to an input of a voltage comparison unit, the other input of which is connected to a storage element which is adapted to store the value of the unknown signal at the instant at which the first switching The surface area below this decaying part is equal to A S(t)dt= 780.

Integration of the twice amplified signal during a finite time 2 results in This must be equal to A, so

TS, 278,, 2'rS e' 75 ZTS 21-8 6 from which it follows that The value of S(t) is then S(t) S e" /2S Consequently, the amplified signal must be integrated until it has decreased to half its initial value, i.e., until it is equal to the initial value of the original, nonamplified signal. This operation can be automatically performed by means of the device having the described construction.

The invention will be described in detail with reference to the accompanying drawing in which.

FIG. 1 shows a block diagram of a device according to the invention,

FIG. 2 shows a circuit diagram ofa part of the device shown in FIG. 1.

FIG. 3 shows a diagram to illustrate the operation of the part of the device shown in FIG. 2,

FIG. 4 shows a circuit diagram of another part of the device shown in FIG. 1,

FIGS. 5 a-d show a number of diagrams to illustrate the voltage variation at different locations in the device shown in FIG. 1, and

FIGS. 6a-6c show a number of block diagrams representing different feasible embodiments of a part of the device shown in FIG. 1.

The embodiment of the device according to the invention, shown in FIG. 1 in the form of a block diagram, comprises an input conductor 1 which can be connected to a detector (not shown), for example, for measuring the concentration of a quantity of dye injected into the blood of a human or animal to be examined. The output signal of such a detector is a voltage which is the electrical analogue of the variation of the quantity to be measured. This unknown signal generally consists of a peak which is followed by a decaying part, the first part of which decreases exponentially, and a next part of which can be distorted by disturbing peaks.

The device further comprises an output conductor 3 which is connected to a first switching member 5. In the position of the first switching member 5 shown in FIG. 1, the output conductor 3 is connected to the input conductor 1. In the other position of this switching member, the output conductor 3 is connected to the output 7 of a signal generator 9 which is adapted to generate an exponentially decreasing signal so as to simulate the decaying part of the unknown signal without the disturbing peaks. The signal generator 9, to be discussed in detail with reference to FIG. 2, comprises a capacitor 11 which can be discharged via a resistance element 13 (both denoted by broken lines in FIG. I). The resistance of the resistance element 13 is dependent on the voltage at a control input 15 of the signal generator 9, so that a variation of this voltage causes a variation of the time constant of the network formed by the capacitor 11 and the resistance element 13.

The capacitor 11 is connected to the incoming conductor 1 via an interruption circuit 17. The interruption circuit 17, to be described in detail herinafter with reference to FIG. 2, constitutes a second, periodically operating switching member which each time establishes a connection between the input conductor I and the capacitor 11 for a given period of time. and which subsequently interrupts this connection again.

Connected between the output 7 of the signal generator 9 and the switching member 5 is an amplifier 19, the function of which will be described hereinafter. The output of the amplifier 19 is also connected to an input 21 of a measuring member 23 which is adapted to determine the difference between the signal generated by the signal generator and the unknown signal. The latter signal can be applied to the measuring member 23 via a second input 25 which is connected to the input conductor 1.

The measuring member 23 comprises a differential amplifier 27, the two inputs of which are connected to the inputs 21 and 25 of the measuring member. By a suitable choice of the resistors 29, 31, 33, 35 and 37, it can be achieved in known manner that the (unknown) signal which enters via the second input 25 is amplified more than the (generated) signal entering via the first input 21, the relationship between the amplification of the two signals being exactly equal to the amplification of the amplifier 19. As a result the voltage appearing on the output 39 of the differential amplifier 27 is proportional to the difference between the signal generated by the signal generator and the unknown signal.

The output 39 of the differential amplifier 27 is connected, via a coupling resistor 41,, to an input 43 of a first integrator 45 which consists of a known network,

comprising an amplifier 47, a capacitor 49 and a resistor 51. The output 53 of this integrator also forms the output of the measuring member 23, and is connected to the control input 15 of the signal generator 9.

The output 39 of the differential amplifier 27 is not only connected to the input 43 of the integrator 45, but also to an indicator 55 which can be, for example, a voltmeter, a lamp or a circuit which is adapted to actuate one or more switching members. The indicator 55 gives an indication when the difference between the unknown signal and the generated signal becomes zero, or reaches another predetermined value.

The amplification of the amplifier 19 is adjusted to the value two by means of resistors 57 and 59. The output of this amplifier is connected to an input 61 of a voltage comparison unit 63, the other input 65 of which is connected to a capacitor 67. The output of the voltage comparison unit 63 is connected to a third switching member 69 in the form of a relay. When the relay 69 is energized, the output conductor 3 is grounded so that this conductor no longer carries a voltage. The operation of the voltage comparison unit will be described with reference to FIG. 4.

The device shown in FIG. 1 also comprises a fourth switching member 71 which can establish a connection between the incoming conductor 1 and the electrode of the capacitor 67 which is connected to the second input 65 of the voltage comparison unit 63. The device further comprises a fifth switching member 73 which connects, in its closed position, the interruption circuit 17 to the capacitor 11 of the signal generator 9, and a sixth switching member 74 by means of which the input 43 of the integrator 45 can be short-circuited. As is shown in FIG. 1, the output conductor 3 is preferably connected to a second integrator 75 which is constructed in the usual manner including an amplifier 77, a resistor 79 and a capacitor 81. The output 83 of the second integrator 75 can be connected, for example, to a write unit, an indicating measuring instrument, or an apparatus for further arithmetical processing (not shown).

FIG. 2 shows a more detailed circuit diagram of the interruption circuit 17 and the signal generator 9. The interruption circuit 17 consists of a switching transistor 85 which is controlled by an astable multivibrator which is formed by the transistors 87 and 89, the capacitors 91 and 93 and theresistors 95, 97, 99 and 101. The operation of such a circuit is generally known and will not be described in detail in this context. The time during which the transistor 87 is conducting is determined by the values of the capacitor 93 and the resistor 101, and the time during which the transistor 89 is conducting is determined by the values of the capacitor 91 and the resistor 99. The choice of the values of these components is, of course, completely dependent on the nature of the unknown signal to be analyzed. For heart minute volume determinations by means of a dye dilution curve, a multivibrator frequency of approximately Hz was found to offer satisfactory results, the transistor 89 then being conducting for about a twentieth part of each period. When transistor 89 is conducting, the base of the switching transistor 85 is connected to the positive supply voltage via a resistor 103, with the result that during this time the switching transistor 85 is also conducting which means that the input conductor is connected, via the fifth switching member 73, to the capacitor 11 of the signal generator 9. The signal generator 9 comprises the capacitor 11 and the resistance element 13 which is connected parallel thereto and which consists of a transistor 105 with a resistor 107 in its collector lead. The base of the transistor 105 is connected, via a resistor 109, to the control input of the signal generator 9 and, via a resistor 111, to a sawtooth generator which also forms part of the signal generator and which is formed by the transistors 113 and 115, the capacitors 117 and 119, and the resistors 121, 123, 125 and 127. The operation of the sawtooth generator will not be described in this context as this circuit is generally known. The voltage generated by the sawtooth generator is supplied, via the resistor 111, to the base of the transistor 105. This voltage V, is shown in FIG. 3 as a function of time. Added to the voltage V, is a direct voltage V, which is applied via the control input 15 and the resistor 109. The transistor starts to conduct as soon as the base voltage exceeds a given value which is denoted in FIG. 3 by V At a given amplitude and frequency of the sawtooth voltage V the time during which the transistor 105 is conducting depends on the control voltage V, as is obvious from FIG. 3. This time is denoted in FIG. 3 by and the-time during which the transistor 105 is not conducting is denoted by t The sum of z and t, is the duration of one period of the sawtooth generator. The effective resistance of the resistance element is then equal to where R is the value of the resistor 111. The time. constant of the network formed by the capacitor 11 and the resistance element 13 is where C is the capacitance of the capacitor 11.

If V, 2 V,, the transistor 105 is continuously conducting which means that t;, 0. In that case, 1' RC. This is the minimum value of r The values of R and C must be chosen such that this minimum value is always smaller than the smallest anticipated time constant of the decaying part of the unknown signal. The frequency of the sawtooth generator must, of course, be so high that t, is always very small with respect to RC. A suitable combination for the recovery of primary dilution curves is found to be formed by an RC- time of 1.5 seconds and a sawtooth frequency of l ,000 Hz. Y

The voltage comparison unit 63 shown in FIG. 4 comprises a known comparator circuit which is composed of the transistors 129 and 131 and the resistors 133 and 135. The collector connections of the transistors are interconnected by a sixth switching member 137 which can be opened so as to start the comparator. The operation is as follows. As long as the voltage on the first input 61 is higher than that on the second input 65, the transistor 129 is conducting and transistor 131 is cutoff. This means that the voltage on the base of an output transistor 139 is comparatively high, so that this transistor is also cut off. If the voltage on the first input 61 becomes lower than that of the second input 65, the transistor 129 is cut off and transistor 131 starts to conduct. When the values of the resistors 133 and are suitably chosen, for example, 100 K0 and 12 KO, respectively, the base voltage of the output transistor 139 decreases very strongly so that this transistor becomes conducting. The collector lead of the output transistor 139 incorporates a coil 141 which forms part of the said relay 69. A limiting resistor 143 is connected in series with the coil 141. As soon as the transistor 139 starts to conduct, the collector current of this transistor flows through the coil 141 with the result that the relay is energized and the output conductor 3 is grounded.

The operation of the device shown in FIG. 1 will now be described with reference to FIG. 5. FIG. 5a shows, by way of example, a dilution curve as usually measured in the determination of the heart minute volume.

A signal voltage V,(t), forming the electrical analogue of the dilution curve, is applied to the incoming conductor 1. This signal has a first peak 145, followed by an exponentially decreasing decaying part having a number in this case two of disturbing recirculation peaks 147 and 149.

Via the interruption circuit 17 and the switching member 73, this voltage is periodically applied to the capacitor 11 with the result that the latter is each time charged until its voltage is equal to the instantaneous value of V,(t). The voltage on the capacitor 11 is denoted by V (t) in FIG. 5a.

The output voltage of the signal generator 9 (the capacitor voltage V ,(t)) is amplified by a factor of two by the amplifier 19 and is subsequently applied to an input of the differential amplifier 27, the second input of which is connected to the incoming conductor 1. Consequently, the original signal V (t) is applied to the second input. As the differential amplifier 27 is adjusted such that the voltage which is applied to its second input is amplified twice as much as the voltage applied to its first input, a voltage V appears on the output 39 of the differential amplifier 27 which is proportional to V,(t) V, (t). This voltage is shown in FIG. b.

The voltage V ,,(t) is integrated and its sign is reversed by the integrator 45, the output voltage V (t) of which is shown in FIG. 5c. This voltage is applied to the control input of the signal generator 9, with the result that the time constant 1 at which the capacitor 11 is discharged changes as described with reference to the FIGS. 2 and 3.

Before V,(t) reaches the first peak 145, V,(t) V (t) is continuously positive, so that V ,,(t) is also continuously positive and V (t) becomes increasingly negative. As a result, V, (see FIG. 3) continuously remains smaller than V,, so that 0, so

This means that the capacitor 11 retains its voltage during the time that it is not connected to the incoming conductor 1, so V (t) remains constant during this time and is only periodically matched to V,(t). As soon as V,(t) has passed the first peak 145, V,(t) decreases so that now V,(t) V (t) and hence V ,,(t) is negative each time. V (t) then starts to increase and at a given instant it reaches a value at which (see FIG. 3) becomes larger than zero. This means that 1- obtains a finite value and the capacitor 11 starts to discharge as soon as it is no longer connected to the incoming conductor 1. The variation of V ,(t) is then as shown at 151 in FIG. 5a.

At a given instant t r is exactly equal to the time constant of the exponentially decreasing decaying part of V,(t) At this time V,(t,,) V 0,) 0, also after the connection between the capacitor 11 and the input conductor 1 has been interrupted, so V 0,) 0. As a result, V,;,( t) remains constant, so that 7 no longer varies either.

The disappearance of V ,,(t) is indicated by the indicator 55, in reaction to which the user of the apparatus can perform an operation by which the switching members 5, 71, 73, 74 and 137 can be simultaneously switched from the position shown in FIG. 1 and FIG. 4, respectively, to the other position. The instant at which this takes place is denoted by t, in FIG. 5. If desired, the

indicator 55 can be constructed to perform the said operation automatically, without human intervention.

Because the switching member 73 is opened, the capacitor 11 can no longer be connected to the incoming conductor 1, so the further variation of V,(t) no longer influences V (t). The closing of the switching member 74 causes the input 43 of the integrator 45 to become voltageless, so that V (t) remains constant in any case.

Due to the opening of the switching member 137 (FIG. 4), the voltage comparison unit 63 is actuated. This unit compares the voltage on the capacitor 67 (equal to V,(t,)) with the output voltage 2V (t) ofthe amplifier 19.

By means of the switching member 5, the output conductor 3 and hence the input of the second integrator 75 is connected to the input conductor 1 until the instant t Consequently, on the output 83 the voltage V (t) (FIG. 5d) varies as the integral of V,(t). At the instant t,,, the switching member 5 is switched over and the output conductor 3 is connected to the output of the amplifier 19. Consequently, as of that instant. V 0) varies as the integral of 2V ,(t). This integration is continued until V (t) reaches a value V... This is the value which V (t) would reach after an infinite time if the non-amplified voltage V ,(t) were applied to the integrator 75. V (t) would in that case vary in accordance with the curve 153 which is denoted by a broken line in FIG. 5d.

Thanks to the amplifier 19, V (t) reaches the value V after a comparatively short time, i.e., at the instant t when the voltage 2V (t) has decreased to half its value at the instant t,,. Because the value V, (t,) is equal to V (t,) at the instant 2,, the instant t, can be determined since at that instant 2V (t,) V,(t,). This instant is determined by the voltage comparison unit 63, one input 61 of which receives the voltage 2V,,(t), while its other input 65 is connected to the capacitor 67 which was connected until the instant 1,, via the switching member 71, to the incoming conductor 1 and which, consequently, has retained the voltage V,(t,) since the instant t At the instant t,, the relay 69 is energized with the result that the outgoing conductor 3 is connected to ground and the input voltage of the integrator, consequently, becomes zero. V (t) remains constant and'equal to V, as of that instant.

The described operations take place only if the signal V,(t) indeed comprises an exponentially decreasing part of sufficient length after the peak 145. If this is not the case, V ,,(t) will never become equal to zero, which is of course noticed by the user. If desired, the indicator 55 can incorporate an alarm device which gives an alarm when V (t) is still not equal to zero after the expiration of a predetermined period of time. This alarm unit can, for example, simultaneously short circuit the output 83 of the integrator 75 so that the device does not provide a measuring result. This is an important advantage of the device according to the invention over other devices which are based on the assumption that there is always an exponentially decreasing part so that they supply an incorrect measuring result if this is not so, for example, because the first recirculation peak 147 appears very early.

If will be obvious that several of the described parts of the device can be readily replaced by other functionally equivalent parts. For example, for the variable resistance element 13 a photosensitive resistor in combination with a controllable light source can be used instead of the circuit described with reference to FIG. 2. The interruption circuit 17 can be readily replaced by an electromechanical switch, for example, a reed relay.

FIG. 6 shows some possible variations of the construction of the measuring member 23. FIG. 6a corresponds to the diagram shown in FIG. 1. The input receives a voltage V (t) which is proportional to V (t) V, (t). One output produces a voltage V (t) which is proportional to V (t) and which can be applied to the indicator 55, while the other output produces a control voltage V,(t) which serves to control the signal generator G and which is equal to In the example of FIG. 6b, the voltage V (t) is directly integrated without insertion of the amplifier 27. The advantage thereof is that any drift in the amplifier 27 does not affect V,(t). In this case If desired, instead of a voltage which is proportional to the integral of V (t) a combination of such a voltage and a voltage that is proportional to V (t) itself can be used as the control voltage V,(t). An example of a circuit for obtaining such a voltage is given in FIG. 6c. Therein, V,(t)=(R /R,,) V (t) +(1/R C I V (t)dt.

As a result, it can in some cases be achieved that the output voltage V (t) of the signal generator 9 adapts itself quicker to the variation of the unknown voltage V,(t).

What is claimed is:

l. A device for simulating the shape of an input signal which includes a peak followed by a decaying part, at least the first portion of said decaying part decreasing exponentially and a subsequent portion of said decaying part being distorted, said device comprising a first switching member, a signal generator adapted to generate an exponentially decreasing signal that simulates the decaying part of the input signal without the distorted portion, means for selectively connecting an outgoingconductor via said first switching member to an incoming conductor which serves to supply the input signal and to the output of said signal generator, said signal generator comprising a capacitor which can be discharged via a resistance element, a second periodically operating switching member for connecting said capacitor to the incoming conductor, means for adjusting the time constant of the network formed by the resistance element and the capacitor so as to match this time constant to that of the decaying part of the input signal, and means for connecting the incoming conductor and the output of the signal generator to first and second inputs, respectively, of a measuring member which derives a difference signal determined by the difference between the amplitudes of the signal generated by the signal generator and the input signal.

2. A device as claimed in claim 1 wherein the measuring member comprises a first integrator for integrating said difference signal, and means connecting the output of said first integrator to a control input of the signal generator, the time constant of the resistorcapacitor network of the signal generator being dependent on the voltage at the control input.

3. A device as claimed in claim 1 further comprising, an amplifier connected between the output of the signal generator and the first switching member, the amplification of said amplifier being equal to two, means connecting the output of the amplifier to an input of a voltage comparison unit, means connecting the other input of the comparison unit to a storage element connected in circuit so as to store the value of the input signal at the instant at which the first switching member interrupts the connection between the incoming and the outgoing conductor, a third switching member, means connecting said voltage comparison unit to actuate the third switching member upon equality of the voltages at its two inputs, and means connecting the third switching member to the outgoing conductor to render same voltageless upon actuation of the third switching member.

4. A device as claimed in claim 2 further comprising an amplifier having an amplification factor of two and connected between the output of the signal generator and the first switching member, a voltage comparator having first and second inputs and an output, means connecting the output of the amplifier to the first input of the comparator, a storage element selectively coupled to the incoming conductor so as to store the input signal appearing thereat at the instant at which the first switching member interrupts the connection between the incoming and outgoing conductors, means connecting the second input of the comparator to the storage element, and a third switching member connected to the output of the comparator and to the outgoing conductor so as to remove the voltage from said outgoing conductor upon actuation of said third switching member caused by equality of the voltages at the first and second inputs of the comparator.

5. A signal simulation device for an input signal having a waveform with a peak followed by a decreasing exponential portion the terminal portion of which is distorted, said device comprising an input line at which the input signal appears and an output line, a signal generator adapted to generate a decreasing exponential signal that simulates the decreasing exponential portion of the input signal but without the distorted terminal portion, first switching means for selectively coupling the output line to the input line and to the output of the signal generator in mutually exclusive time intervals, said signal generator including an RC time constant network with a control input for adjusting the value of said time constant to vary the exponential waveform of said signal generator, a switching member for periodically connecting said RC network to the input line, and means coupled to the input line and the signal generator output and responsive to the signals thereat for deriving a control signal determined by the difference between the amplitudes of the signal generator output signal and the input signal.

6. A device as claimed in claim 5 further comprising means responsive to said control signal for signalling said switching means to switch the connection of the output line from said input line to the output of the signal generator when said control signal achieves a predetermined value.

7. A device as claimed in claim 6 further comprising means for modifying said control signal to derive a second control signal, and means for applying said'second control signal to the control input of said RC network to vary the RC time constant thereof as a function of said second control signal.

8. A device as claimed in claim 7 further comprising means controlled by the input signal appearing on the input line at the instant said switching means switches the output line to the output of the signal generator and by the output signal of the signal generator for coupling the output line to a point of fixed potential upon equality of the input signal and the signal generator output signal.

. 75; UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent 3,859,602 Dated January 7, 1975 Inventor) FRITS JACQUES JANSSEN ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

. v IN THE TITLE PAGE 1 cancel "723463 and insert 7203463 Engncd and Sealed this seventh Day of October 1975 [SEAL] Attest:

. RUTH C. MASON c. MARSHALL DANN Attestmg Oj/zcer Commissioner ujPaIents and Trademarks 

1. A device for simulating the shape of an input signal which includes a peak followed by a decaying part, at least the first portion of said decaying part decreasing exponentially and a subsequent portion of said decaying part being distorted, said device comprising a first switching member, a signal generator adapted to generate an exponentially decreasing signal that simulates the decaying part of the input signal without the distorted portion, means for selectively connecting an outgoing conductor via said first switching member to an incoming conductor which serves to supply the input signal and to the output of said signal generator, said signal generator comprising a capacitor which can be discharged via a resistance element, a second Periodically operating switching member for connecting said capacitor to the incoming conductor, means for adjusting the time constant of the network formed by the resistance element and the capacitor so as to match this time constant to that of the decaying part of the input signal, and means for connecting the incoming conductor and the output of the signal generator to first and second inputs, respectively, of a measuring member which derives a difference signal determined by the difference between the amplitudes of the signal generated by the signal generator and the input signal.
 2. A device as claimed in claim 1 wherein the measuring member comprises a first integrator for integrating said difference signal, and means connecting the output of said first integrator to a control input of the signal generator, the time constant of the resistor-capacitor network of the signal generator being dependent on the voltage at the control input.
 3. A device as claimed in claim 1 further comprising, an amplifier connected between the output of the signal generator and the first switching member, the amplification of said amplifier being equal to two, means connecting the output of the amplifier to an input of a voltage comparison unit, means connecting the other input of the comparison unit to a storage element connected in circuit so as to store the value of the input signal at the instant at which the first switching member interrupts the connection between the incoming and the outgoing conductor, a third switching member, means connecting said voltage comparison unit to actuate the third switching member upon equality of the voltages at its two inputs, and means connecting the third switching member to the outgoing conductor to render same voltageless upon actuation of the third switching member.
 4. A device as claimed in claim 2 further comprising an amplifier having an amplification factor of two and connected between the output of the signal generator and the first switching member, a voltage comparator having first and second inputs and an output, means connecting the output of the amplifier to the first input of the comparator, a storage element selectively coupled to the incoming conductor so as to store the input signal appearing thereat at the instant at which the first switching member interrupts the connection between the incoming and outgoing conductors, means connecting the second input of the comparator to the storage element, and a third switching member connected to the output of the comparator and to the outgoing conductor so as to remove the voltage from said outgoing conductor upon actuation of said third switching member caused by equality of the voltages at the first and second inputs of the comparator.
 5. A signal simulation device for an input signal having a waveform with a peak followed by a decreasing exponential portion the terminal portion of which is distorted, said device comprising an input line at which the input signal appears and an output line, a signal generator adapted to generate a decreasing exponential signal that simulates the decreasing exponential portion of the input signal but without the distorted terminal portion, first switching means for selectively coupling the output line to the input line and to the output of the signal generator in mutually exclusive time intervals, said signal generator including an RC time constant network with a control input for adjusting the value of said time constant to vary the exponential waveform of said signal generator, a switching member for periodically connecting said RC network to the input line, and means coupled to the input line and the signal generator output and responsive to the signals thereat for deriving a control signal determined by the difference between the amplitudes of the signal generator output signal and the input signal.
 6. A device as claimed in claim 5 further comprising means responsive to said control signal for signalling said switching means to switch The connection of the output line from said input line to the output of the signal generator when said control signal achieves a predetermined value.
 7. A device as claimed in claim 6 further comprising means for modifying said control signal to derive a second control signal, and means for applying said second control signal to the control input of said RC network to vary the RC time constant thereof as a function of said second control signal.
 8. A device as claimed in claim 7 further comprising means controlled by the input signal appearing on the input line at the instant said switching means switches the output line to the output of the signal generator and by the output signal of the signal generator for coupling the output line to a point of fixed potential upon equality of the input signal and the signal generator output signal. 